Spread of Bighorn Sheep Pneumonia Continues

The deadly spread of pneumonia in Montana’s bighorn sheep population
picked up momentum west of Anaconda, where a hunter alerted Fish,
Wildlife & Parks of possible disease in the Lost Creek population.
Biologists killed four sheep and confirmed through lab work they were
infected. FWP announced the latest outbreak today, which occurred in the
sixth bighorn sheep population in west central Montana.

FWP, in its killing of suspected sick sheep, is continuing an
experimental and aggressive battle against the easily spread and usually
fatal respiratory disease.

“We’re too early in this to know everything we’d like to know. But,
until we are able to survey and collect more sheep, we have to proceed
as if we are dealing with a pneumonia outbreak,” said FWP Wildlife
Biologist Ray Vinkey. “We can’t afford to miss the chance of removing
the last sick sheep before they infect the rest of the population. Right
now we’re taking it one day at a time.”

A hunter, Wayne Estay of Butte, first reported signs of sick sheep west
of Anaconda during a preseason scouting trip on Aug. 17.

Vinkey and another FWP wildlife biologist, Jay Kolbe, responded and shot
the sheep that exhibited clinical signs or behavior suggesting
pneumonia. According to an FWP news release, they collected blood and
tissue samples for further analysis at the FWP wildlife lab in Bozeman.
Autopsies showed everything from early to advanced infection in the
lungs, which in the worst case had also compromised the heart and liver.
The varying stages of infection suggest that the disease is spreading
over time.

Other pneumonia outbreaks affected bighorn populations in the East Fork
of the Bitterroot late last fall and in the Bonner area and Lower and
Upper Rock Creek herds in January and February. Most recently FWP
detected pneumonia in the Skalkaho population east of Hamilton on Aug. 9
(see NewWest’s story).

Last fall, FWP began killing sick sheep from the East Fork and Bonner
populations to try to protect healthy animals. Officials allowed the
disease to run its course in Lower Rock Creek, however, due to terrain
and difficulty in finding and approaching the bighorns there. The
disease also ran its course in Upper Rock Creek, where it was too
widespread to try to control. Bighorns wandering to or from Rock Creek
could have spread the disease to the Anaconda herd this summer, but the
source may never be proven, according to FWP.

“Our experience so far in the East Fork of the Bitterroot demonstrates
that killing sick sheep can succeed in saving the rest of the
population,” said Mike Thompson, FWP Region 2 Wildlife Manager. “This
kind of work is hard on everyone. But, the key is early detection and a
quick, aggressive response.”

Chris Anderson, a student volunteer with FWP from the University of
Minnesota, documented the survival of 32 lambs per 100 ewes in the East
Fork this summer, where FWP removed 80 sick individuals last fall and
winter, and at least 87 seemingly healthy sheep remain. But where FWP
let the disease run its course last winter, Anderson was unable to find
any lambs that had survived exposure to the pathogens persisting in Rock
Creek bighorns. He reports landowners have found dead lambs and sick
adults in that area this summer.

The Lost Creek herd was established in 1967, with help from the Anaconda
Sportsmen’s Club, when 25 bighorns were transplanted from the Sun River
herd. More than half of the population was lost to pneumonia in 1991,
but has since recovered to number at least 297 sheep. Twelve hunters
hold either-sex licenses and 30 hold ewe-licenses for this hunting
district, which are valid beginning Sept. 5. FWP will contact hunters as
more becomes known about the outbreak.

There have been no known cases of humans or pets contracting pneumonia
from wild sheep, but FWP cautions anyone who finds dead or sick bighorn
sheep to leave the animal alone. FWP also encourages the public to
immediately report any observations of sheep exhibiting symptoms of an
illness or strange behavior.

“Reports from the public were responsible for the first detection of
pneumonia in most of our recent outbreaks,” said Vinkey. “These reports
from the public help us determine how widespread the sickness is and
give us a chance at catching it in its early stages.”